package com.drug.mingkang.utils;

/**
 * 描述:雪花算法工具类
 *
 * @author wcj
 * @version 1.0
 * @date 2019/12/2 11:42
 */
public class Snowflake {
        private long workerId; // 这个就是代表了机器id
        private long datacenterId; // 这个就是代表了机房id
        private long sequence; // 这个就是代表了一毫秒内生成的多个id的最新序号
        public Snowflake(long workerId, long datacenterId, long sequence) {
            // sanity check for workerId
            // 这儿不就检查了一下，要求就是你传递进来的机房id和机器id不能超过32，不能小于0
            if (workerId > maxWorkerId || workerId < 0) {

                throw new IllegalArgumentException(
                        String.format("worker Id can't be greater than %d or less than 0",maxWorkerId));
            }

            if (datacenterId > maxDatacenterId || datacenterId < 0) {

                throw new IllegalArgumentException(
                        String.format("datacenter Id can't be greater than %d or less than 0",maxDatacenterId));
            }
            this.workerId = workerId;
            this.datacenterId = datacenterId;
            this.sequence = sequence;
        }
        private long twepoch = 1288834974657L;
        private long workerIdBits = 5L;
        private long datacenterIdBits = 5L;

        // 这个是二进制运算，就是5 bit最多只能有31个数字，也就是说机器id最多只能是32以内
        private long maxWorkerId = -1L ^ (-1L << workerIdBits);
        // 这个是一个意思，就是5 bit最多只能有31个数字，机房id最多只能是32以内
        private long maxDatacenterId = -1L ^ (-1L << datacenterIdBits);
        private long sequenceBits = 12L;
        private long workerIdShift = sequenceBits;
        private long datacenterIdShift = sequenceBits + workerIdBits;
        private long timestampLeftShift = sequenceBits + workerIdBits + datacenterIdBits;
        private long sequenceMask = -1L ^ (-1L << sequenceBits);
        private long lastTimestamp = -1L;
        public long getWorkerId(){
            return workerId;
        }
        public long getDatacenterId() {
            return datacenterId;
        }
        public long getTimestamp() {
            return System.currentTimeMillis();
        }
        // 这个是核心方法，通过调用nextId()方法，让当前这台机器上的snowflake算法程序生成一个全局唯一的id
        public synchronized long nextId() {
            // 这儿就是获取当前时间戳，单位是毫秒
            long timestamp = timeGen();
            if (timestamp < lastTimestamp) {
                System.err.printf(
                        "clock is moving backwards. Rejecting requests until %d.", lastTimestamp);
                throw new RuntimeException(
                        String.format("Clock moved backwards. Refusing to generate id for %d milliseconds",
                                lastTimestamp - timestamp));
            }

            // 下面是说假设在同一个毫秒内，又发送了一个请求生成一个id
            // 这个时候就得把seqence序号给递增1，最多就是4096
            if (lastTimestamp == timestamp) {

                // 这个意思是说一个毫秒内最多只能有4096个数字，无论你传递多少进来，
                //这个位运算保证始终就是在4096这个范围内，避免你自己传递个sequence超过了4096这个范围
                sequence = (sequence + 1) & sequenceMask;
                if (sequence == 0) {
                    timestamp = tilNextMillis(lastTimestamp);
                }

            } else {
                sequence = 0;
            }
            // 这儿记录一下最近一次生成id的时间戳，单位是毫秒
            lastTimestamp = timestamp;
            // 这儿就是最核心的二进制位运算操作，生成一个64bit的id
            // 先将当前时间戳左移，放到41 bit那儿；将机房id左移放到5 bit那儿；将机器id左移放到5 bit那儿；将序号放最后12 bit
            // 最后拼接起来成一个64 bit的二进制数字，转换成10进制就是个long型
            return ((timestamp - twepoch) << timestampLeftShift) |
                    (datacenterId << datacenterIdShift) |
                    (workerId << workerIdShift) | sequence;
        }
        private long tilNextMillis(long lastTimestamp) {

            long timestamp = timeGen();

            while (timestamp <= lastTimestamp) {
                timestamp = timeGen();
            }
            return timestamp;
        }

        public String code(){
            String result="";
            for(int i=0;i<6;i++){
                int intVal=(int)(Math.random()*26+97);
                result=result+(char)intVal;
            }
            return result;
        }

        private long timeGen(){
            return System.currentTimeMillis();
        }
        //---------------测试---------------
        public static void main(String[] args) {

            Snowflake snowflake = new Snowflake(1,1,1);
            String code = snowflake.code();
            System.out.println(code);
        }

}
